Australian authorities hacked Tor users in the US as part of a child pornography investigation, Motherboard has learned.

The contours of this previously-unreported hacking operation have come to light through recently-filed US court documents. The case highlights how law enforcement around the world are increasingly pursuing targets overseas using hacking tools, raising legal questions around agencies’ reach.

In one case, Australian authorities remotely hacked a computer in Michigan to obtain the suspect’s IP address.